Process for the preparation of trans, cis, trans-1, 2, 4-tricarboxy-cis-3-carboxymethylocylopentane



United States The present invention relates to a new alicyclictetracarboxylic acid and to its dianhydride. More particularly, thepresent invention relates to a new geometric isomer ofl,2,4-tricarboxy-3-carboxymethylcyclopentane and to the dianhydridethereof.

The four ring substituents of l,,4-tricarboxy-3-carboxyrnethylcyclopentane may be arranged in a varietyof ditferent configurations with respect to each other depending uponwhich side of the plane of the alicyclic nucleus they are situated. Thepresent invention involves the 1,2,4 tricarboxy 3carboxymethylcyclopentane in which a pair of the ring substituents lieon one side of the alicyclic nucleus and the remaining pair lie on theopposite side. in this arrangement, it may be said that one pair of thering substituents are trans with respect to the other pair. According tothis terminology, the new acid of the present invention may bedesignated as trans,cis,trans-l,2,4 tricarboxy cis 3carboxymethylcyclopentane. Another, perhaps more appropriate manner ofnaming this compound is with the use of parenthetical arrows to indicatethe relative positions of the various ring substituents. According tothis system of nomenclature, the new isomer of the present inventionwould be l(l),2(t),4(l)-tricarboxy-3(*U-carboxymethylcyclopentane.

may be represented by the following structural formula:

coon GHECOOH '0 on o 0 on in which the two substituents attached to thering by solid lines lie on the same side of the plane of the ring whichis opposite to the side on which the substituents attached by dottedlines lie.

it is an object of the present invention to prepare a novel isomer ofl,2,4-tricarboXy-3-carboxymethylcyclopentane having the configurationrepresented by l(l),2(' ),4(l)-tricarboxy-B(T)-carboxymethylcyclopentane. it is a further object toprepare the dianhydride of l(J/),2( *),4(l)-tricarboxy-S(T)-carboxymethylcyclopentane. It is a still further objectof the invention to prepare these compounds from relatively cheap,readily available starting materials. Other and additional objects willbecome apparent from a consideration of the ensuing specification andclaims.

Broadly speaking, I prepare the new isomer of 1,2,4-tricarboXy-3-carboxymethylcyclopentane by oxidizing or-hydroxy-S,fi-dihydroexo-dicyclopentadiene (hereinafter referred togenerally as dicyclopentcnyl alcohol) or the carboxylic acid estersthereof. Dicyclopentenyl alcohol may be obtained by direct hydration ofdicyclopenta diene which, in turn, is readily available in commercialquantities from the high temperature cracking of natural gas andpetroleum oils as well as from coal tar. The oxidation may be performedwith nitric acid or other suitable oxidizing media in the presence ofsuitable catalysts. The invention is illustrated by the followingexamples:

7 Example 1 A mixture of 3909 grams of 70% nitric acid and 3.0

Diagrammatically, this compound v atet Efitid ice iii

a. grams of vanadium pentoxide was heated to 60 C. and 1.0 gram ofsodium nitrite was thereafter added to tmixture. The resultant solutionwas agitated while 35 grams of dicyclopentenyl alcohol was addeddropwise at atmospheric pressure over a period of 12 hours while thetemperature was maintained at 60 C. T he exothermic nature of thereaction was sufficient to maintain this operating temperature;occasional cooling being required to prevent the temperature fromrising. After addition of the alcohol was complete, the solution wasallowed to simmer at 60 C. for two hours and was then concentrated byremoving 640 grams of distillate under reduced pressur Upon completionof the concentrating, the pot temperature was a little below 50 C. Thesolution was cooled and seeded with 1(l),2(T),4(l)-tricarboxy-3(1-)-carboxymethylcyclopentane and permitted to stand undisturbed overnight.The following day, 92 grams of solid product were removed by filtration.Additional product was recovered later on by further concentrationutilizing the same procedure.

The product, a white solid, was washed with glacial acetic acid anddried. It was then recrystallized from additional glacial acetic acid.The compound had a melting point of 136-187 C. It was identified byneutral equivalent and infrared absorption techniques as l(l),2(1),4(-l) tricarboxy 3Q) carboxymethylcyclopentane.

Example 2 Three thousand parts of 70% nitric acid was heated to 55 C.and a few grains (a pinch) of sodium nitrite was added. Then 353 partsof dicyclopentenyl alcohol was added dropwise, with stirring, over 3hours at a rate such that the temperature of the mixture did not riseabove 60 C. After being stirred for two additional hours at 55-60 C.,the reaction mixture was concentrated, at reduced pressure, to a totalweight of approximately 1500 parts. After the mixture stood for 2-3days, the solids which separated were collected on a sintered glassfunnel and sucked as dry as possible. The filter cake was slurried with157 parts of acetic acid, filtered, and washed with two 50-part portionsof acetic acid. After drying, the white product which weighed 181 parts(29.9% conversion) melted at 1824 C. Recrystallization from 142 parts ofboiling acetic acid gave 148 parts (82% recovery) of1(l),2(),4(l)-tricarboxy-3(t)-carboxymethylcyclopentane which melted at186l87 C.

Example 3 A pinch of sodium nitrite was added to 3,000 grams of 70% HNOheated to 59 C, and 450 grams of 5- or6-acetorry-dihydro-exo-dicyclopentadicnc was added dropwise over 3hours, the temperature being maintained at 5560 C. he reaction mixturewas concentrated under reduced pressure, and the product crystallizedout upon standing. After slurrying in acetic acid, 19 1.5 grams ctmaterial melting at l8l-4 C. was obtained. Upon recrystallization fromboiling acetic acid, the melting point was raised to 187-8 C., and theproduct was i entitled as 1(l),2(1),4(J/) tricarboxy 30p) carboxymethylyclopcntane.

Bicyclopenteuyl alcohol may be prepared from clicyclopentadiene with2.125% sulfuric acid according to the technique of Bruson and Rienerdescribed in I. Am. Chem. Soc. vol. 67, pages 723-3 (1945). The alcoholis used for the oxidation step rather than the dicyclopentadiene itselfbecause the latter tends to polymerize and char in an oxidizingenvironment.

The carboxylic acid esters of dicyclopentenyl alcohol may be obtained bydirect esteriiication of the alcohol or by the sulfuric acid catalyzedaddition of the acid to dicyclopentadiene, as described in I. Am. Chem.Soc, vol.

sesame 31 67, pages 11784180 (1945). Thus, the starting material ofExample 2 may be prepared from dicyclopentadiene and acetic acid, or bydirect esteriiication of dicyclopen tenyl alcohol with acetic acid. Theester group does not enter into the reaction, and the new compound ofthe present invention may thus be prepared from dicyclopentenyl alcoholand/or from any ester thereof which is hydrolyzable to the alcohol. Thenature or structure of the ester group, i.e., of the acid from which theester is prepared, is in no sense critical to the invention. Foreconomic reasons, the esters of simple, readily-available aliphatic andaromatic acids, like acetic acid and benzoic acid, are preferredstarting materials as is the dicyclopentenyl alcohol itself.

For the oxidation, nitric acid having an initial concentration of about30-75% is operable. With nitric acid below about 30% concentratiomthereaction is too slow to be of any practical significance. Nitric acidstronger than about 75% tends to overoxidize the alcohol which leads tothe formation of oxalic acid. Though oxidation with nitric acidrepresents the preferred procedure, other conventional oxidizing agentsare operable including, for example, chromic acid and the like. I

A catalyst is not essential to the oxidation. It is often veryadvantageous, however, since the presence of a catalystwill frequentlyaccomplish better yields at lower temperatures, and sometimes with lessnitric acid than would otherwise be required. Suitable catalysts includepulverized cobalt, nickel or vanadium, as well as the oxides ofvanadium, tantalum, lead, manganese, cobalt, chromium, and molybdenum,etc.

it has also been found that sodium nitrite tends to promote the reactionby initiating the formation of oxides of nitrogen which tend toencourage the oxidation, as is well-known in the art. This is not acritical feature of the invention, however, inasmuch as the oxidationmay be carried out in the absence of sodium nitrite as well as Without acatalyst.

Once addition of the dicyclopentenyl alcohol is commenced, thetemperature of the reaction mass must be kept below about 75 C. This isnecessary in order to prevent overoxidati'on. The reaction'may beconveniently performed anywhere in the range of about 30 to 60 C. andthis represents the preferred opera-ting range. Atmospheric pressure issuitable though increased pressure may facilitate the reaction in someinstances.

Best yields are obtained if the reaction mass is maintained at theoperating temperature for at least about an hour after the addition ofthe dicyclopentenyl alcohol is' completed. In a batch system, theinitial run may occasionally not result in the precipitation of anyproduct presumably because of the solubility of the product in thereaction mass. In such cases the reaction mixture may be butted back toabout 70% nitric acid, based on the water present, and the oxidizingprocedure repeated. At this time, solids begin to appear and the productmay be isolated by filtration as indicated above. Subsequent repetitionof the oxidation procedure by fortifying the nitric acid to about a 70%concentration each time will give additional product until all of thedicyclopentenyl alcohol has been converted. An alternative method forisolating product from a first-run oxidation mixture yielding noprecipitate is to strip oif dilute nitric by distillation until theproduct precipitates suiliciently :to be filtered, as illustrated inExample 1.

1(l),2(),4(l) tricarboxy 3(1) carboxymethylcyclopentane is a white solidmelting at 136-187 C. It is soluble in water and in lower aliphaticalcohols as well as in hydrochloric and glacial ace-tic acids.

The dianhydride of the acid is somewhat difficult to prepare due to thepresence of the methylene group be tween the carboxyl groups in the 1-and 4-positions. I have found, however, that it is possible to preparethe dianhydride by stirring the free acid with a large excess of acetylchloride, acetic anhydride or otherdehydrating 6. agents for very longperiods. The preparation of the dranhydricle by this technique isillustrated by the following example:

Example 4 One part of l(l),2(1),4(l)-tricarboxy-3(N-carboxymethylcyclopentane is treated wtih 20 partsof acetyl chloride by stirring at room temperature for 3 to 5 weeks. Theresulting solution is concentrated under vacuum to complete dryness. Theresidue is siurried in a small amount of acetyl chloride. Theundissolved product is filtered off and washed with benzene. Thediauhydride of 1(l),2(1),4(l)-tricarboxy-3(fl-carboxymethylcyclopentanewas obtained in a 39.5% yield, based on the 1 l) ,2 t) ,4 l-tricarboxy-3 (1- -carboxymethylcyclopentane. It melted at l70l72 C. Thedianhydride can be converted back to the original acid by hydrolysis.

The tetra'butyl ester of 1(l),2(t),4(l)-tricarboxy-3(T)-curboxymethylcyclopentane, which may be formed by esterification ofl(l),2(),(4(l) -tricarboxy-3(1)- carboxymethyicyclopentane withn-butanol, may be used as aplasticizer for nitrocellulose. Thedianhydride which is'al'so made from the free acid, for example, by thetechnique described above, is useful as curing agents for epoxy resins.The cure may be eifected by mixing the dianhydride with the resin atmoderate temperatures and thereafter'curing the mixture in a mold atelevated temperatures, usually in the neighborhood of about 200 C., fora number of hours. The following example illustrates a typical epoxycure which is effected with the dianhydride of 1(l) ,2(T),4(-l)-tricarboxy-3 (1) -carboxymethylcyclopentane.

Example 5 Twenty grams of a typical commercial epoxy resin sold by theCiba Co. as Araldite 6020 and formed by the condensation ofepiehlorohydrin with 4,4-isopropylidenediphenol is mixed with 5.68 gramsof the dian'hydride of 1(l),2(1 ),4(l)-tricarboxy-3(1-)-carboxymethylcyclopentane at C. for 10 minutes to givean anhydride/epoxide ratio of 0.55/1. The dispersion was then cured in amold at 200 C. for 24 hours to give a hard, light brown resin having aheat distortion temperature of 153 C. at 264 p.s.i. fiber stress. Theresin showed a flexural strength of 7328 p.s.i. at room temperature, anda fiexural modulus of 044x10 p.s.i. at room temperature. The cured resinis useful as a molding or potting composition, etc.

I have described and illustrated my invention in the foregoingspecification. Since many variations maybe made in practicing theinvention without departing from the spirit or scope thereof I intend tobe limited only by the following claims.

I claim:

1. A. process for the preparation of trans,-cis,trans-1,2,4-t-ricarboxy-cis-3 carboxymethylcyclopcntane which comprisesreacting a com-pound selected from the group consisting of (A)S-hydrox-y-S,d-dihydro-exo-dicyclopentadiene, (B) 6-hydroxy-5,6-dihydro-exo-dicyclopentadiene, (C) the acetic acid ester of5-hydroxy-5,6-dihydro-exo-dicyclopentadiene, (D) the acetic acid esterof 6-dihydroxy-5,6 -dihydro-exo-dicyclopentadiene, (E) the benzoic acidester of 5 hydroXy-S,6-dihydro-exo-dicyclopentadicne and (F) the benzoicacid ester of 6- hydroxy-5,6-dihydro-exo-dicyclo-pentadiene with aqueousnitric acid of a concentration in the range of from about 30% to about75%, at a temperature below about 75 C.

2. The process of claim 1 wherein said compound isS-hydroxy-S,6-dihydro-exo-dicyclopentadiene.

3. The process of claim 1 wherein said compound is6-l1ydroxy-5,6-dihydro-exo-dicyclopentadiene.

4. The process of claim 1 wherein said compound is the acetic acid esterof 5-hydroxy-5,6-dihydro-exo-dicyclopentadiene.

5. The process of claim 1 wherein said compound is the acetic acid esterof 6-hydroxy-5,6-dihydro-exo-dicyclopentadiene.

6. The process of claim 1 wherein said compound is the benzoic acidester of S-hydroxy-S,6-dihydro-exo-dicyclepentadiene.

References Cited in the file of this patent UNITED STATES PATENTSPerkins et a1. May 22, 1934 Greenlee Oct. 21, 1952 Greenlee Feb. 9, 1954Fischer et a1 June 12, 1956 6 Muetterties Feb. 19, 1957 Linn July 2,1957 Elam et a1. July 2, 1957 Finch et a1 Sept. 10, 1957 OTHERREFERENCES

1. A PROCESS FOR THE PREPARATION OFTRANS,CIS,TRANS1,2,4-TRICARBOXY-CIS-3 - CARBOXYMETHYLCYCLOPENTANE WHICHCOMPRISES REACTING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF (A)5-HYDROXY-5,6-DIHYDRO-EXO-DICYCLOPENTADIENE, (B) 6-HYDROXY-5,6 -DIHYDRO-EXO-DICYCLOPENTADIENE, (C) THE ACETIC ACID ESTER OF5-HYDROXY-5,6-DIHYDRO-EXO-DICYCLOPENTADIENE, (D) THE ACETIC ACID ESTEROF 6-DIHYDROXY-5,6 - DIHYDRO-EXO-DICYCLOPENTADIENE, (E) THE BENZOIC ACIDESTER OF 5-HYDROXY-5,6-DIHYDRO-EXO-DICYCLOPENTADIENE AND (F) THE BENZOICACID ESTER OF 6HYDROXY-5,6-DIHYDRO-EXO-DICYCLO-PENTADIENE WITH AQUEOUSNITRIC ACID OF A CONCENTRATION IN THE RANGE OF FROM ABOUT 30% TO ABOUT75%, AT A TEMPERATURE BELOW ABOUT 75*C.